1. Field of the Invention
The present invention relates to the field of equipment for installing optical access networks. In particular, the present invention relates to an optical branching device suitable for separating optical fibres extracted from a riser cable of an optical access network.
2. Description of the Related Art
An optical network of the type known as FTTP (“Fibre To The Premises”) or FTTH (“Fibre To The Home”) is an optical access network which supplies a number of end users with broadband or ultra-wideband communications services, in other words services which require data transmission speeds of several hundreds of Mbit/s or even higher speeds.
Typically, an FTTP or FTTH optical network comprises a distribution box which is typically positioned in the basement of the building in which the end users reside.
An optical cable, which will be referred to hereafter as a “riser cable”, emerges from the distribution box and runs vertically inside the building from the basement to each floor. The riser cable comprises a plurality of optical fibres, typically up to 96 optical fibres, enclosed in an outer sheath. The riser cable is typically laid in a channel which provides mechanical protection for the cable. This channel can be fixed to the surface of a wall or can be housed in the thickness of the wall (in the concrete, for example). Inside the channel, the riser cable can run together with other cables, such as power distribution cables and telephone cables.
On each floor of the building, the optical riser cable typically passes through junction boxes together with the electrical and telephone cables.
In the portion of riser cable housed in the junction box, an access window can be cut in the riser cable sheath and one or more optical fibres can be extracted from it. Each extracted optical fibre can then be inserted into a corresponding protective tube known as a “drop tube”, and can be extracted from the junction box and routed towards the apartment of a user residing on the floor in question. At any intermediate point between the access window and the user's apartment, the extracted optical fibre, protected by the tube, can be joined to a user optical cable, known as a “drop cable”, which can be “pre-connectorized”, meaning that it has an optical connector on its free end. The pre-connectorized end of the user cable is typically located in a suitable termination box in the user's apartment, in such a way that the user can connect it directly to his devices which use broadband services (such as a PC and a set-top box).
US 2010/0232752 describes an optical branching device suitable for receiving a portion of a riser cable in the sheath of which an access window has been cut to extract one or more optical fibres. The device has two shells at its opposite ends, which bear on the sheath of the riser cable. At the ends of the device there are also channels for receiving a strap or tape which partially surrounds the outer circumference of the shell and partially surrounds the circumference of the sheath of the riser cable, thus fixing the device to the cable. Between the shells, the device has a longitudinal recess which can be aligned with the access window in the sheath, thus exposing the optical fibres of the cable. The device also includes six outlet ports for guiding the optical fibres extracted from the cable. The ports are positioned obliquely with respect to the longitudinal recess.